1. Field of the Invention
The present invention relates to a mould for manufacturing an annular object of elastic material, preferably a sealing ring, having a reinforcing element which is completely or partially embedded in said object.
2. Description of the Prior Art
Sometimes it is desirable to provide sealing rings manufactured from rubber or another rubber elastic material with different kinds of reinforcing elements of rigid material, for example metals or hard plastic materials. For example the reinforcing elements can have purpose of improving the retaining of such sealing rings which are adapted for the sealing of pipes in the grooves formed in the pipe walls. Thereby, the sealing rings are prevented from being pushed out from the grooves when the pipe joints are mounted or from being blown out from the pipe joints when the differences between the pressures at each side of the joints are great. It is previously known either to provide the sealing rings with reinforcing elements which are connected with the rings after the manufacturing thereof or even after the sealing rings have been positioned in the grooves in the pipe wall or to provide the sealing rings with reinforcing elements which are connected with the sealing rings while the rings are manufactured and which can be completely or partially embedded in the material of the sealing rings.
Recently, it has also been proposed to position sealing rings provided with reinforcing elements in grooves in the pipe walls by forming the pipe walls around the sealing rings, whereby the sealing rings themselves will form the grooves in which the rings are positioned. This method of forming the grooves of the pipe walls and concurrently position the sealing rings provided with reinforcing elements in the grooves has been used especially in connection with plastic pipes. Thereby, a sealing ring which is provided with a reinforcing element is positioned on a forming mandrel, whereupon the plastic pipe wall which has been softened by means of heating is pushed over the mandrel and the sealing ring positioned thereon. The pipe wall is formed around the outer peripheral surface of the sealing ring for forming a groove which partially receives the sealing ring. After the pipe wall has been cooled and solidified the pipe wall is removed from the mandrel, the sealing ring thereby being retained in the groove. Because of the fact that the sealing ring is provided with a reinforcing element the sealing ring will be securely retained in the groove.
Especially in connection with the last mentioned method of positioning a sealing ring provided with a reinforcing element in the groove of the pipe wall it is of great importance that the reinforcing element is connected with the sealing ring in a correct and exact way.
For manufacturing an annular object of elastic material, preferably a sealing ring, having a reinforcing element which is completely or partially embedded in the object it is previously known to use a mold, in which the reinforcing element is positioned before the elastic material is supplied to the mold, said mold having support surfaces for supporting the reinforcing element in the mold. Thereby, it is a considerable problem to position and retain the reinforcing element in the mold in such an exactly predetermined way which is required for providing an acceptable final product, i.e. the sealing ring provided with a reinforcing element. In order to obtain an acceptable result it is not only required that the support surfaces of the mold are formed in a correct way but also that the reinforcing element is manufactured with extremely small tolerances. The last-mentioned requirement has been difficult to comply with, as it is necessary to manufacture the reinforcing elements from a material which is easy to work, preferably metal wire, unless the reinforcing element is not too expensive. However, there are substantial difficulties in using materials which are easy to work for the manufacturing of reinforcing elements having small tolerances. Another drawback is that reinforcing elements manufactured from such materials are easily deformed after the manufacturing thereof.
When manufacturing sealing rings provided with reinforcing elements by means of the previously known molds it is time-consuming to position the reinforcing elements in the mold cavity, and it has also occurred that the reinforcing element has taken a position outside the mold cavity so that the mold has been damaged during the closing thereof.
Thus, there exist substantial problems with regard to the manufacturing of sealing rings having reinforcing elements by means of the molds which are now used.